The objective of our research is to study the dynamics of reactions catalyzed by heme enzymes and to obtain information about the structures of catalytic intermediates formed during catalysis. The information obtained will be used to formulate specific chemical mechanisms of action for these enzymes. The studies will focus on horseradish peroxidase, catalase, cytochrome c peroxidase and lactoperoxidase. Comparisons will also be made with myoglobin. To elucidate the complete mechanism of an enzyme, a detailed description of the elementary steps in the catalytic pathway is essential. Of central importance is the active site structure of the enzyme in these intermediates, since this reveals how catalysis is brought about. To achieve these goals, two current approaches are being combined. Stopped flow cryoenzymology is being used to detect and stabilize specific intermediates in solution. Resonance Raman spectroscopy is being employed to selectively examine the vibrational spectrum of the heme group in the catalytic intermediates. The resonance Raman spectra provide information about the oxidation and spin state of the heme iron, the nature and strength of the iron-axial ligand bonds and the electron distribution of the heme group and the axial ligands. From this data, detailed mechanisms of action will be formulated for these peroxidases.